Firearm cartridge

ABSTRACT

A firearm cartridge has a case defining an interior chamber and having a case mouth, an elongated projectile having a forward end and a rear end, a sabot assembly having an exterior sized to be closely received in the case mouth, and defining an interior passage adapted to closely receive the projectile, and the projectile including a stabilizer at the rear end. The stabilizer may include fins. The projectile may include a circumferential groove at an intermediate portion between the forward end and rear end. The sabot assembly includes a mating feature adapted to engage the circumferential groove to limit axial motion of the projectile with respect to the sabot assembly. The projectile may define a plurality of circumferential grooves. The sabot assembly may include a plurality of mating features adapted to engage the circumferential grooves. The sabot assembly may include a plurality of elements arranged about the projectile.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/541,994 filed on Aug. 7, 2017, entitled“SELF-STABILIZED PROJECTILES,” and claims the benefit of U.S.Provisional Patent Application No. 62/619,365 filed on Jan. 19, 2018,entitled “NON-RIFLE/SHOTGUN (NRS) FIREARM SYSTEM,” which are herebyincorporated by reference in its entirety for all that is taught anddisclosed therein.

FIELD OF THE INVENTION

The present invention relates to cartridges for projectile weapons and,more particularly, to a cartridge including a drag-stabilizedprojectile.

BACKGROUND OF THE INVENTION

The National Firearms Act of 1934 (NFA) requires the registration withthe federal government of machineguns, rifles and shotguns having anoverall length less than 26 inches, rifles with a barrel shorter than 16inches, and shotguns with a barrel length less than 18 inches. Anexample of a prior art short barreled rifle is shown in FIG. 1. Shortbarreled rifles are appealing for interior home defense and other closequarters battle applications where a longer barrel could be difficult tomaneuver or easily snagged. The NFA definition of a rifle includes a“rifled barrel,” and the NFA definition of a shotgun includes a “smoothbore.” Similarly, many state “assault weapon” regulations define anassault weapon as having either a smoothbore or rifled barrel. Thus, anopportunity exists to create a firearm that does meet the legaldefinition of a rifle or a shotgun, making it not subject to thesefederal or state regulations.

An example of a firearm technology that is not classified as a pistol,rifle, or shotgun by the NFA is a firearm having a barrel with straightcut lands and grooves. In the 1870s, Husqvarna Vapensfabrik of Swedenmade shotguns with this feature. Verney-Carron SA of makes shotgunbarrels with straight cut lands and grooves sold under the Hastingsbrand name. Briley of Houston, Tex. makes straight cut choke tubes.Roughly five hundred years ago, muzzle loading barrel manufacturersoriginally made straight cut lands and grooves with the intent ofdepositing carbon in the bore to allow for more shots before needing toclean. This eventually led to the rifle with spiral cut barrels. Soonafter, the straight cut barrels were abandoned in favor of the othertechnology. The only reason Swedish shotguns had this design was so theycould be used to hunt in the King's forest (who declared that smoothbore weapons could not be used.) The reason why Hastings and Briley usestraight cut land and groove shotgun components is to keep the wads fromspinning and therefore keeping the shot column moving forward with lessdispersion from angular momentum upon exiting the muzzle. Except forthis specialized usage, barrels with straight cut lands and grooves havebeen viewed as an obsolete firearms technology because of the increasedprojectile velocity and accuracy resulting from rifles. Furthermore, abarrel with straight cut lands and grooves has never been used with amodern breech-loading, metallic cartridge.

Therefore, a need exists for a new and improved firearm cartridge thatincludes a drag-stabilized projectile that increases the accuracy of afirearm barrel with straight cut lands and grooves. In this regard, thevarious embodiments of the present invention substantially fulfill atleast some of these needs. In this respect, the firearm cartridgeaccording to the present invention substantially departs from theconventional concepts and designs of the prior art, and in doing soprovides an apparatus primarily developed for the purpose of providing adrag-stabilized projectile that increases the accuracy of a firearmbarrel with straight cut lands and grooves.

SUMMARY OF THE INVENTION

The present invention provides an improved firearm cartridge, andovercomes the above-mentioned disadvantages and drawbacks of the priorart. As such, the general purpose of the present invention, which willbe described subsequently in greater detail, is to provide an improvedfirearm cartridge that has all the advantages of the prior art mentionedabove.

To attain this, the preferred embodiment of the present inventionessentially comprises a case defining an interior chamber and having acase mouth, an elongated projectile having a forward end and a rear end,a sabot assembly having an exterior sized to be closely received in thecase mouth, and defining an interior passage adapted to closely receivethe projectile, and the projectile including a stabilizer at the rearend. The stabilizer may include fins. The projectile may include acircumferential groove at an intermediate portion between the forwardend and rear end. The sabot assembly includes a mating feature adaptedto engage the circumferential groove to limit axial motion of theprojectile with respect to the sabot assembly. The projectile may definea plurality of circumferential grooves. The sabot assembly may include aplurality of mating features adapted to engage the circumferentialgrooves. The sabot assembly may include a plurality of elements arrangedabout the projectile. There are, of course, additional features of theinvention that will be described hereinafter and which will form thesubject matter of the claims attached.

There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood and in order that the presentcontribution to the art may be better appreciated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front isometric view of a prior art short barreled riflesubject to regulation by the National Firearms Act.

FIG. 2 is a side sectional view of the current embodiment of the firearmbarrel constructed in accordance with the principles of the presentinvention.

FIG. 3 is a rear view of the current embodiment of the firearm barrel ofFIG. 2.

FIG. 4 is a front view of the current embodiment of the firearm barrelof FIG. 2.

FIG. 5 is an exploded view of the current embodiment of a firearmcartridge constructed in accordance with the principles of the presentinvention and suitable for use with the firearm barrel of FIG. 2.

FIG. 6 is a left side view of the projectile of FIG. 5 removed from thefirearm cartridge.

FIG. 7 is a left side sectional view of the firearm cartridge of FIG. 5in the assembled state. The dashed lines at the nose show a conventionalbullet profile.

FIG. 8 is a front view of the firearm cartridge of FIG. 5 in theassembled state.

FIG. 9 is a right side sectional view of the projectile and sabot ofFIG. 5 with the sabot in the process of separating from the projectileduring flight.

FIG. 10 is a rear isometric view of a first alternative embodiment of aprojectile suitable for use with the firearm barrel of FIG. 2.

FIG. 11 is a rear isometric view of a second alternative embodiment of aprojectile suitable for use with the firearm barrel of FIG. 2.

The same reference numerals refer to the same parts throughout thevarious figures.

DESCRIPTION OF THE CURRENT EMBODIMENT

An embodiment of the firearm cartridge of the present invention is shownand generally designated by the reference numeral 200.

FIGS. 2-4 illustrate the improved firearm barrel 10 of the presentinvention. More particularly, the firearm barrel is an elongated bodyhaving a rear/breech end 12 and an opposed muzzle end 14. The barreldefines a barrel bore 16, which communicates with a chamber 18 in therear end, and a barrel axis 24. In the current embodiment, the barrel ischambered to receive a 0.308 Winchester cartridge. However, the barrelcan be chambered for any suitable cartridge, including 300 Blackout and5.56 mm. The entire barrel bore forward of the chamber has an interiorsurface 26 having a plurality of alternating lands 20 and grooves 22(the lands and grooves extend from the chamber to the muzzle end, givingthe bore a constant cross-sectional profile along its length). Thegrooves are surfaces separated from the bore axis by a first radius. Thelands are surfaces separated from the bore axis by a second radius lessthan the first radius. In the current embodiment, there are six straightlands and six straight grooves with a 0.300 inch bore diameter and a0.308 inch groove diameter. The grooves are each 0.123+0.002/−0.000 inchwide with no twist to provide a minimum bore and groove area of 0.0736sq. in. However, the barrel bore can have a diameter of between 0.17inch and 0.50 inch depending on what size cartridge the barrel ischambered to receive. The chamber is sized to centerfire cartridgehaving a bottlenecked case, but can also be sized to receive a rimfirecartridge.

The lands 20 and grooves 22 are straight elements parallel to the boreaxis in the current invention, such that no spin is imparted to aprojectile (not shown) propelled down the barrel bore 16. However,compared to propelling an identical projectile down a smoothbore barrel(not shown), the lands and grooves prevent yawing of the projectilewithin the firearm barrel 10. Deforming the projectile with the landsalso has the benefit of creating a known pressure profile. There is noevidence the straight lands and grooves decrease the velocity of aprojectile propelled through the firearm barrel 10 compared to aconventional rifled barrel. While the accuracy of a projectile propelledthrough the firearm barrel 10 can be decreased compared to the accuracyof a projectile propelled through the conventional short barreled rifle100 shown in FIG. 1, 5.56 mm rounds are still accurate to within 3 to 4MOA at 50 yards, which is sufficient for interior home defense and otherclose quarters battle applications. Conventional 300 Blackout ammunitionis accurate to within 3 MOA at 100 yards. The ammunition is relativelyaccurate given the 11.5 inch length of the firearm barrel 10, but theprojectiles are unstable and prone to tumbling in flight. As a result,the projectiles may hit the target sideways.

It should be appreciated that the firearm barrel 10 is adapted to beattached to a conventional firearm frame/upper receiver to form acomplete firearm that is not subject to regulation by the NationalFirearms Act even if the length of the firearm barrel 10 is less than 16inches, or the complete firearm has a total length less than 26 inches.For example, the firearm barrel 10 can be substituted for theconventional short rifle barrel 102 shown in FIG. 1 and used with theconventional upper receiver 104, lower receiver 106, and stock 108 alsoshown in FIG. 1 to form a complete firearm.

In some applications of the firearm barrel 10, much greater accuracythan 3 MOA at 100 yards is required. In these circumstances, a firearmcartridge 200 including a drag-stabilized projectile 216 is highlydesirable. Moreover, the straight lands 20 and grooves 22 of the firearmbarrel 10 enable finned and flared ammunition to be fired in a stablefashion. The rifled bore of a conventional short barreled rifle 100would be unsuitable for this purpose because the rifling woulddestabilize a projectile that was designed to be spin stabilized. Asmoothbore barrel would also destabilize a projectile that was designedto be spin stabilized. Furthermore, the firearm barrel 10 does not loseany of the energy from discharge by spinning the projectile within thefirearm barrel 10. Instead, all the energy of discharge can used topropel the projectile in a linear fashion at a higher velocity, which isbelieved to provide the projectile with superior penetrative propertiesupon encountering a target, and/or with less barrel wear.

FIGS. 5-8 illustrate the improved firearm cartridge 200 and projectile216 of the present invention. More particularly, the firearm cartridgeis sized for use in a barrel chambered in 300 Blackout in the currentembodiment. The firearm cartridge includes a case 202 having a front204, rear 206, and exterior 208. The front defines a case mouth 210 thatcommunicates with an interior chamber 212 and a neck 284. The exteriorincludes a bottlenecked portion 214 located below the case mouth.

An elongated projectile 216 having a tapered forward end 218 and a rearend 220 has the rear end received within the interior chamber 212 of thecase 202. The projectile includes a stabilizer 222 at the rear end,which is a plurality of fins 224 in the current embodiment. The exterior226 of the projectile defines a first circumferential groove 228, secondcircumferential groove 230, and third circumferential groove 232. Thethree circumferential grooves are all located between the forward endand the rear end of the projectile. The first circumferential groove islocated at an intermediate portion 234, and the second and thirdcircumferential grooves are located rearward of the firstcircumferential groove.

A sabot assembly 236 has an exterior 238 sized to be closely received inthe case mouth 210 and defines an interior passage 240 adapted toclosely receive the projectile 216. The sabot assembly includes aplurality of identical elements/petal segments 242 that are arrangedabout the projectile. In the current embodiment, the sabot assembly hasthree petal segments, but any suitable number of segments could be used.Each petal segment has an interior 244 that defines a plurality ofmating features 246 adapted to engage the circumferential grooves 228,230, 232 on the projectile to limit axial motion of the projectile withrespect to the sabot assembly. In the current embodiment, the matingfeatures are ridges 248 and grooves 250. Each petal segment has aforward rim 252 that is spaced apart from the projectile. Each petalsegment has a forward end portion 254 that encompasses the projectileand includes a tapered groove 256 that defines a gap with respect to theprojectile. Each petal segment defines a linear channel 258 parallel tothe length of the projectile. In the current embodiment, the linearchannel has a semi-cylindrical surface 260 and an open forward end 262.The linear channel separates opposed and elongated contact surfaces 264adapted to contact the projectile.

In the current embodiment, the projectile 216 has a length 270 of 1.485inch and the intermediate portion 234 is located at the midpoint of theprojectile. The projectile has a diameter 272 of 0.150 inch over themajority of the projectile's length. The linear channels 258 of thepetal segments 242 have a length 274 greater than the length of theprojectile. The linear channels of the petal segments also have a lengthgreater than the diameter of the projectile and the diameter 276 of thecase mouth 210. The linear channels also have a length that is at leasthalf the length 280 of each petal segment. The centers of thecircumferential grooves 228, 230, 232 are separated from one another by0.125 inch. The center of circumferential groove 228 is located 0.810inch from the tapered forward end 218 of the projectile. Thecircumferential grooves 228, 230, 232 reduce the diameter of theprojectile to 0.120 at their centers. The tapered forward end has alength of 0.101 inch. The diameter of the projectile at the base of thetapered forward end flares slightly to 0.156 inch compared to thediameter of the remainder of the projectile's length. The fins 224 havea diameter of 0.290 inch that is less than the diameter of the straightlands 20 of the firearm barrel 10 (0.300 inch). The fins are 0.070 inchwide. The sabot assembly 236 has a diameter that is large enough toengage the straight lands of the firearm barrel 10, which prevents thesaboted projectile from slightly rotating under launch conditions.Unlike conventional spin-stabilized projectiles, fin stabilizedprojectiles like projectile 216 are negatively influenced by rotating inflight since it increases yaw and instability. By not inducing spin onthe projectile 216, the firearm barrel 10 makes the projectile moreaccurate than it would be if fired from a conventional rifled firearmbarrel 102. In FIG. 7, the dashed lines 266 show a conventional bulletprofile relative to the forward end 218 of the projectile 216. Thedashed lines 268 show powder that is received within the interiorchamber 212 of the case 202. A portion of the powder surrounds the rearend 220 of the projectile, including the fins 224.

In FIG. 7, the dashed lines 266 show a conventional bullet profilerelative to the forward end 218 of the projectile 216. The dashed lines268 show powder that is received within the interior chamber 212 of thecase 202. A portion of the powder surrounds the rear end 220 of theprojectile, including the fins 224.

FIG. 9 illustrates the improved projectile 216 and sabot assembly 236 inflight. After the projectile and sabot assembly exit the muzzle end 14of the firearm barrel 10, the forward rims 252 of the petal segments 242act as air wedges because the forward rims are chamfered inward and peelthe petal segments away from the projectile. Wind resistance alsocreates a pressure wave down the length of the linear channels 258,which then spreads laterally at the blind rear ends 282 of the linearchannels to spread the interiors 244 of the petal segments away from theexterior 226 of the projectile without affecting the flight of theprojectile. The separation of the petal segments without affecting theflight of the projectile is believed to increase accuracy of theprojectile. The ridges 248 of the petal segments are concave/toroidalwith concave mating surfaces that provide a hinging relationship withthe circumferential grooves 228, 230, 232. Eventually, these effectscombine to separate the petal segments from the projectile, which thenflies unencumbered to its target.

The circumferential grooves 228, 230, 232 are all positioned either ator behind the longitudinal midpoint/intermediate portion 234 of theprojectile 216 because the circumferential grooves add drag duringflight. Because of their position, the circumferential grooves add dragonly to the rear half of the projectile, thereby preserving orincreasing the projectile's drag-induced aerodynamic stability. If anyof the circumferential grooves were located on the front half of theprojectile, they would instead impart aerodynamic instability to theprojectile. The fins 224 also provide rear drag that keeps the forwardend 218 of the projectile pointed forward during flight. Thiscombination of elements moves the center of pressure rearward of theprojectile's center of gravity, which is believed to enable theprojectile to be launched without experiencing inaccuracy issuesassociated with transonic flight instability. The circumferentialgrooves are also located where they are to lock in the petal segments242 at the case neck 284. To maximize the powder capacity in theinterior chamber 212 of the case 202 to result in the highest possiblemuzzle velocity of the projectile, the circumferential grooves are alsolocated to ensure that as much of the projectile as possible is locatedoutside the case mouth while still fitting within a conventionalcartridge profile required to fit in a standard magazine. In addition,the sabot assembly 236 has a shorter overall length than the projectile.By having a shorter overall length, the projectile can be seated in thecase to the normal specified seating depth without impinging on thecase's powder capacity.

It should be appreciated that the firearm cartridge 200, using aconventional 300 Blackout case 202 with regular powder 268 and a regularprimer (not shown), results in the projectile 216 fired through thefirearm barrel 10 achieving sub-MOA accuracy. In testing, the projectilehas produced five shot groups of less than 1 inch at 100 yards. Thisexceeds the accuracy achieved by conventional bullets fired fromBlackout 300 cartridges and propelled through a conventional rifledfirearm barrel 102 measuring 11.5 inches, as well as the accuracy ofmost AR-type rifles.

FIG. 10 illustrates a first alternative embodiment of the improvedprojectile 300. More particularly, the projectile 300 has a bulbous,forward weighted front half 302 and a lighter, drag-inducing finned tailrear half 304. The overall diameter of the front and rear halves aresubstantially similar with the rear half being no larger than the fronthalf. The front half has a drive band 306 that is sized so theprojectile will obturate when it encounters the straight lands 20 andgrooves 22 of the rifle barrel 10 to increase pressure.

In the current embodiment, the projectile 300 has a length of 1.224inch. The distance from the front of the front half 302 to the driveband is 0.298 inch. The driveband has a length of 0.1 inch and adiameter of 0.308 inch. The diameter of the forwardmost portion of thefinned tail rear half 304 is 0.158 inch. The distance from the front tothe location where the finned tail rear half begins to flare outwardfrom the front half 302 is 0.644 inch. The maximum diameter of thefinned tail rear half is 0.301 inch.

FIG. 11 illustrates a second alternative embodiment of the improvedprojectile 400. More particularly, the projectile 400 has a bulbous,forward weighted front half 402 and a lighter, drag-inducing revolvedradius face rear half 404. The front and rear halves are joined by aneck portion 406. The overall diameter of the front and rear halves issubstantially similar with the rear half being no larger than the fronthalf. The front half has a diameter that is sized so the projectile willobturate when it encounters the straight lands 20 and grooves 22 of therifle barrel 10 to increase pressure.

In the current embodiment, the projectile 400 has a length of 0.598inch. The maximum diameter of the front half 402 is 0.308 inch, which isgreater than the diameter of the straight lands 20 of the firearm barrel10 (0.300 inch). The distance from the front of the front half 402 tothe narrowest portion of the neck portion 406 is 0.356 inch. Thenarrowest portion of the neck portion 406 has a diaeter of 0.179 inch,which is maintained over a distance of 0.007 inch. The distance from thefront of the front half 402 to the forwardmost portion of the rear half404 is 0.534 inch. The rear half 404 has a maximum diameter of 0.308inch, which is greater than the diameter of the straight lands 20 of thefirearm barrel 10 (0.300 inch).

The projectiles 300, 400 attain their aerodynamic stability byintentionally biasing the mass toward the front half of the projectileand intentionally biasing the drag toward the rear half of theprojectile. The front half possesses more mass than the rear half, andtherefore is the main body of the projectile. The main body has a slopeto the front the decreases aerodynamic drag and a portion behind theslope that extends for some distance before reducing to a significantlysmaller diameter portion in the rear half of the projectile called thetail. As is exemplified by projectiles 300, 400, the tail is a means ofdrag such as a set of fins, ribs, or a revolved radius face. Unlikeprior art drag-stabilized projectiles, the drag features do not extendpast the limits of the main body of the projectile. The projectilestherefore have a profile such that they can be launched accurately fromthe firearm barrel 10 without the assistance of a sabot assembly, whichdecreases manufacturing cost, especially if they can be of unitaryconstruction from a single material. Furthermore, the projectiles have amass comparable to commonly marketed spin-stabilized projectiles of thesame caliber and fit as a direct replacement for a spin-stabilizedprojectile into existing firearm cartridge designs for spins-stabilizedprojectiles.

While a current embodiment of a firearm cartridge has been described indetail, it should be apparent that modifications and variations theretoare possible, all of which fall within the true spirit and scope of theinvention. With respect to the above description then, it is to berealized that the optimum dimensional relationships for the parts of theinvention, to include variations in size, materials, shape, form,function and manner of operation, assembly and use, are deemed readilyapparent and obvious to one skilled in the art, and all equivalentrelationships to those illustrated in the drawings and described in thespecification are intended to be encompassed by the present invention.

Therefore, the foregoing is considered as illustrative only of theprinciples of the invention. Further, since numerous modifications andchanges will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction and operationshown and described, and accordingly, all suitable modifications andequivalents may be resorted to, falling within the scope of theinvention.

I claim:
 1. A firearm cartridge comprising: a case defining an interiorchamber and having a case mouth; an elongated projectile having aforward end and a rear end; a sabot assembly having an exterior sized tobe closely received in the case mouth, and defining an interior passageadapted to closely receive the projectile; and the projectile includinga stabilizer at the rear end.
 2. The firearm cartridge of claim 1wherein the stabilizer includes fins.
 3. The firearm cartridge of claim1 wherein the projectile includes a circumferential groove at anintermediate portion between the forward end and rear end.
 4. Thefirearm cartridge of claim 3 wherein the sabot assembly includes amating feature adapted to engage the circumferential groove to limitaxial motion of the projectile with respect to the sabot assembly. 5.The firearm cartridge of claim 3 wherein the projectile defines aplurality of circumferential grooves, and wherein the sabot assemblyincludes a plurality of mating features adapted to engage thecircumferential grooves.
 6. The firearm cartridge of claim 1 wherein thesabot assembly includes a plurality of elements arranged about theprojectile.
 7. The firearm cartridge of claim 1 wherein the sabotassembly includes a forward rim, and where the forward rim is spacedapart from the projectile.
 8. The firearm cartridge of claim 1 whereinthe sabot assembly has a forward end portion encompassing the projectileand defining a gap with respect to the projectile.
 9. The firearmcartridge of claim 1 wherein the sabot assembly has a forward endportion encompassing the projectile and defining a tapered groove withrespect to the projectile.
 10. The firearm cartridge of claim 1 whereinthe sabot assembly defines a linear channel parallel to the length ofthe projectile.
 11. The firearm cartridge of claim 10 wherein the linearchannel is an elongated channel having a length greater than thediameter of the projectile.
 12. The firearm cartridge of claim 10wherein the linear channel is an elongated channel having a lengthgreater than the diameter of the case mouth.
 13. The firearm cartridgeof claim 10 wherein the linear channel is an elongated channel having alength at least (half?) of a length of the sabot assembly.
 14. Thefirearm cartridge of claim 10 wherein the linear channel has asemi-cylindrical surface.
 15. The firearm cartridge of claim 10 whereinthe linear channel has an open forward end.
 16. The firearm cartridge ofclaim 1 wherein the sabot includes a plurality of petal segments. 17.The firearm cartridge of claim 16 wherein each segment of the sabotassembly defines a linear channel parallel to the length of theprojectile.
 18. The firearm cartridge of claim 17 wherein the linearchannel separates opposed elongated contact surfaces adapted to contactthe projectile.
 19. The firearm cartridge of claim 16 including at leastthree petal segments.